An in vitro method for making repeated pH measurements on human dental plaque.

A combination pH micro-electrode inserted into human plaque centrifuged to the base of a closely-fitting fine-mesh wire "basket" has been used to make continuous recordings of the pH responses produced by exposure to various carbohydrate substrates. The pH depressions given by continued immersion in sugar and starch solutions resemble, both in depth and duration, those obtained by telemetric pH measurements of approximal plaque samples. In contrast, brief exposure to sugar solutions will produce a Stephan type of pH curve. Measurements of pH can be made using a succession of different substrates if, after each substrate is tested, the electrode-plaque assembly is washed with water and its acidity neutralized in circulating saliva. It is suggested that this in vitro pH method could be used instead of the telemetric measurements of approximal plaque for comparing acid production from foods or for other purposes.